This project is concerned with the identification and quantitative description of the contributions of the principal spinal afferent projection systems (a) to the activity of the individual neurons comprising Somafic sensory areas I and II (S-I and S-II, respectively) of the primate cerebral cortex; and (b) to the highly detailed representations of the body which are found within S-I and S-II. Specifically, the proposed studies will employ the techniques of single unit analysis and surgical ablation to determine if the multiple somatic afferent systems contribute differentially (a) to the fine structure of the cortical representation of the body, and/or to the cortical representation of stimulus features in the electrical activity of the individual cortical neurons.